Infrared emitters, which are devices that transmit or “emit” infrared radiation, are utilized in a variety of different applications. For example, infrared emitters are utilized in electronic countermeasures systems such as in the “jamming” of an infrared heat seeking missile for the purpose of protecting an aircraft containing the emitter. FIG. 1 illustrates a countermeasures situation in which a missile 10 attacks an aircraft 12. The missile 10 has a detector assembly 14 which is responsive to infrared radiation in the mid-infrared region. The mid-infrared region may be defined as infrared radiation having wavelengths in the range of 2 to 5 microns, but the specific definition may vary and other times is considered to be infrared radiation having wavelengths 1.3 to 3 microns. The aircraft 12 has jet engines 16, one of which is shown, which emit radiation in the form of infrared radiation in the mid-infrared region. As the missile 10 approaches the aircraft 12, the detector assembly 14 detects the infrared radiation emitted by the aircraft engines 16. The detector assembly 14 develops directional control signals which guide the missile toward the aircraft 12.
The aircraft 12 includes an infrared countermeasures system 18 containing an infrared emitter (not shown) which emits mid-infrared radiation in the form of a sequence of pulses 20 that diverge and propagate towards the missile 10 as indicated by the arrows 22. The missile detector assembly 14 detects the pulses 20 along with the mid-infrared radiation detected from the engines 16. The pulses 20 cause the detector assembly 14 to develop erroneous directional control signals that direct the missile 10 away from the aircraft 12, resulting in a successful countermeasures operation by saving the aircraft from impact of the missile.
Presently available infrared emitters are unduly large and heavy, which results in an undesirable increase in the size and weight of the countermeasures system 18 containing the emitter. A larger and heavier countermeasures system 18 is undesirable because, for example, such a system may not fit into available space within an aircraft and may adversely affect the flight capabilities of the aircraft 12. Some older countermeasures systems 18 included cesium arc lamps or incandescent heat sources for generating the required mid-infrared radiation. Due to the relatively low intensity of the emitted radiation, the emitter in such countermeasures systems 18 has a large reflector to gather and to collimate the radiation to provide a beam of adequate intensity to jam the missile. Such a reflector may have to be mounted partially or completely on the outside of the aircraft 12, introducing excessive drag particularly at high aircraft speeds. To improve countermeasures systems 18, lasers have been utilized in place of cesium arc lamps or incandescent heat sources. Various types of lasers have been utilized in countermeasures systems 18, including semiconductor lasers to reduce the size and weight of and improve the overall performance of the system. Any of these conventional systems 18, particularly those utilizing semiconductor lasers, have difficulties generating mid-infrared radiation having sufficient power to jam the missile 10 at long ranges from the aircraft 12.
There is a need therefore for a mid-infared laser having a compact size that generates mid-infared radiation having high power sufficient to jam missiles at long ranges.